Pd-Ga Alloys Research Articles

Plasma catalytic non-oxidative methane conversion to hydrogen and value-added hydrocarbons on zeolite 13X

Non-thermal plasma has unfolded highly efficient, safe to operate novel routes for methane conversion to hydrogen. In this work, methane conversion is performed under atmospheric dielectric barrier discharge (DBD) plasma with and without 13X zeolite-based catalysts i.e., 13X, Ga/13X, Pd/13X, and Pd-Ga/13X. Experimental results indicate that the plasma catalytic process delivered almost twofold higher product yield than the plasma only route. The binary Pd-Ga catalyst possesses highest catalytic performance with about 40 % CH4 conversion at an input flowrate of 5 cm3min−1 and 2 W due to the formation of the Pd-Ga alloy, which acts as catalytic active centre for activating C–H bonds. Product yield can be tailored by the catalyst design where the bimetallic Pd-Ga/13X preferably favours the hydrocarbon formation while H2 is the dominant product obtained over the Pd/13X. The cleavage of C–H bonds of methane molecule over the plasma only route is mainly governed by energetic electrons in the gaseous phase the catalyst activity, and plasma-catalyst synergism play a significant role in the plasma catalysis process. The findings from this work provide significant insights into the methane activation for subsequent optimization of the methane conversion processes operated on floating production, storage, and offloading vessels (FPSOVs). Exploiting untapped offshore natural gas reserves, where conventional pipeline systems are less economical.

Atomically Thick Oxide Overcoating Stimulates Low-Temperature Reactive Metal-Support Interactions for Enhanced Catalysis.

Reactive metal-support interactions (RMSIs) induce the formation of bimetallic alloys and offer an effective way to tune the electronic and geometric properties of metal sites for advanced catalysis. However, RMSIs often require high-temperature reductions (>500 °C), which significantly limits the tuning of bimetallic compositional varieties. Here, we report that an atomically thick Ga2O3 coating of Pd nanoparticles enables the initiation of RMSIs at a much lower temperature of ∼250 °C. State-of-the-art microscopic and in situ spectroscopic studies disclose that low-temperature RMSIs initiate the formation of rarely reported Ga-rich PdGa alloy phases, distinct from the Pd2Ga phase formed in traditional Pd/Ga2O3 catalysts after high-temperature reduction. In the CO2 hydrogenation reaction, the Ga-rich alloy phases impressively boost the formation of methanol and dimethyl ether ∼5 times higher than that of Pd/Ga2O3. In situ infrared spectroscopy reveals that the Ga-rich phases greatly favor formate formation as well as its subsequent hydrogenation, thus leading to high productivity.

Strong metal–support interaction between palladium and gallium oxide within monodisperse nanoparticles: self-supported catalysts for propyne semi-hydrogenation

The strong metal–support interaction (SMSI) between metals and reducible supports (e.g., CeO2, TiO2, and SnO2), which has been widely investigated, plays a very important role in heterogeneous catalysis. We report the first example of SMSI between palladium (Pd) and gallium oxide (Ga2O3) within a PdGa nanoparticle (denoted as PdxGay NP, where x:y is the atomic ratio of Pd and Ga). The typical features of classic SMSI, such as electron transfer between Ga2O3 and Pd and suppression of H2 and CO adsorption, are successfully observed on PdxGay NPs. Detailed characterizations and control experiments demonstrate that the coexistence of PdGa alloy and Ga2O3 in PdxGay NPs plays a vital role in the formation of SMSI. To systematically study the effects of SMSI on catalytic performance, PdxGay NPs were used as “self-supported catalysts” for propyne semi-hydrogenation (PSH), a critical process for removing trace propyne from propylene in industry. It is shown that optimized Pd0.34Ga1 NPs give a propylene selectivity of 98.2% at a propyne conversion of 96.6% at 30 °C and atmospheric pressure, which is much higher than that of pure Pd NPs and Pd/Ga2O3 catalysts prepared by a conventional wet-impregnation method. The reaction paths of PSH on PdxGay NPs have been further revealed by density functional theory (DFT) calculations. This work may not only deepen the basic understanding of SMSI, but also promote the design and application of heterogeneous catalysts.

Novel sensor to investigate microstructural contributions to corrosion of high‐palladium dental alloys

AbstractThere is incomplete understanding of corrosion mechanisms for high‐palladium dental alloys used for metal‐ceramic restorations. This investigation employed two complementary techniques as a novel sensor for an initial investigation of corrosion tendencies for phases in representative high‐Pd alloys with Pd–Cu–Ga and Pd–Ga compositions. After the initial oxidation step and simulated porcelain‐firing cycles, specimens were polished for examination by Scanning Kelvin Probe Force Microscopy and Atomic Force Microscopy to evaluate the Volta potential difference across the surfaces and correlate potential differences with microstructural phases. The Ru‐rich phase, present in high‐Pd alloys from use of Ru as a grain‐refining element, was clearly more noble than the Pd solid solution matrix in the Pd–Cu–Ga alloys but had much less Volta potential difference than the matrix in the Pd–Ga alloy. Other precipitates in the alloy microstructures had minimal observable differences in Volta potential compared to the matrix. While high‐Pd alloys have been found previously to show excellent overall in vitro corrosion resistance, the Ru‐rich phase may cause localized galvanic corrosion in Pd–Cu–Ga alloys leading to potentially problematic Pd ion release, but have less effect on corrosion in Pd–Ga alloys.

Pd-Ga model SCALMS: Characterization and stability of Pd single atom sites

We have prepared model systems for Pd-Ga supported catalytically active liquid metal solutions (SCALMS) by physical vapor deposition of Pd and Ga in ultrahigh vacuum onto highly oriented pyrolytic graphite (HOPG) pre-modified by Ar+ bombardment. Combining AFM and IRAS with CO as a probe molecule, we investigate the growth behavior, the morphology, the surface chemistry, and the stability of Pd-Ga alloys on HOPG.Our results prove the single atom character of the active sites in Ga-rich Pd-Ga alloys. We show that upon interaction with CO, Ga is displaced from the surface and CO adsorbs in on-top position on surface Pd atoms. Experimental data on the vibrational frequencies and binding energies of CO are compared to the results of DFT calculations for CO adsorption on four different Pd-Ga models, i.e. PdGa(1 0 0), PdGa(1¯1¯1¯), Pd-doped α-Ga(0 0 1), and Pd-doped fcc-Ga(1 0 0). The comparison suggests that widely separated Pd sites are formed in the Ga matrix.

Frontispiece: Spectroscopic Observation and Molecular Dynamics Simulation of Ga Surface Segregation in Liquid Pd–Ga Alloys

Frontispiece: Spectroscopic Observation and Molecular Dynamics Simulation of Ga Surface Segregation in Liquid Pd–Ga Alloys

Spectroscopic Observation and Molecular Dynamics Simulation of Ga Surface Segregation in Liquid Pd-Ga Alloys.

Liquid binary Pd-Ga alloys with low Pd contents of 0.8, 1.8, and 4.7 at % of Pd were examined as a function of sample temperature in ultra-high vacuum by using angle-resolved XPS. Upon cooling from 750 to 400 K, a pronounced temperature-dependence of the Pd concentration in the liquid phase was observed, which was explained by the transition from the pure liquid phase to a two-phase system, consisting of a solid Ga5 Pd phase and a Pd-depleted liquid Pd-Ga alloy. In the liquid Pd-Ga alloy, Pd is always depleted from the topmost interface layer, as deduced from angle-resolved XPS at 0 and 80° emission, independent of temperature and Pd concentration. This observation is interpreted as an inhomogeneous depth distribution function of Pd, that is, the segregation of Ga to the surface of the liquid phase. The results of a DFT-based molecular dynamics simulation (MD) independently show interfacial stratification of Ga and an inhomogeneous Pd distribution along the surface normal. The evaluation of the experimental data with a rigid layer model based on the MD calculations leads to excellent agreement with the simulation.

Self-organization of palladium nanoislands on GaN and AlxGa1−xN/GaN heterostructures

We report on systematic study on the dewetting process of thin Pd layer and self-organized Pd nano-islands on SiO2, GaN and AlxGa1−xN/GaN heterostructures with various Al content. The influence of factors such as the thickness of metal layer, type of top layer of AlGaN/GaN heterostructures, temperature and time of annealing process on the dimensions, shapes and density of Pd islands was analyzed. Comparing the behavior of self-organization of Pd islands on Al0.25Ga0.75N/GaN and SiO2 we can conclude that solid-state dewetting process on SiO2 occures much faster than on Al0.25Ga0.75N. For substrates with SiO2 this process requires less energy and can arise for thicker layer. On the Al0.25Ga0.75N surface the islands take more crystalline shape which is probably due to surface reconstruction of Pd-Ga alloy thin layer on interface. For thin metal layer the coalescence of islands into larger islands similar to Ostwald ripening mechanism was observed. Greater surface roughness of AlxGa1−xN/GaN heterostructures with higher Al content causes an increase of surface density of islands and the reduction of their sizes which improves the roundness. In case of GaN and AlxGa1−xN layers with Al content lower than 20%, the surface degradation caused by annealing process was observed. Probably, this is due to the decomposition of layers with gallium droplet formation on catalytic metal islands.

EXAFS study of model Pd/Ga2O3 catalysts for the liquid-phase hydrogenation of acetylene before and after the reaction

The catalytic characteristics of Pd/Ga2O3 samples in the liquid-phase hydrogenation of acetylene to ethylene are studied. The structure of the catalyst’s components before and after the reaction is examined by EXAFS spectroscopy. The activity of the original (after drying) samples results from the reduction of the original palladium oxide to a metallic state in the reaction medium. According to EXAFS, the catalysts reduced at 200°C contain small amounts of Pd-Ga alloy that was preserved in the reaction medium during the liquid-phase hydrogenation of acetylene and presumably increased the activity and selectivity of the samples.

EXAFS study of Pd/Ga2O3 model catalysts of selective liquid-phase hydrogenation of acetylene to ethylene

Model catalysts Pd/Ga2O3 of selective liquid-phase hydrogenation of acetylene to ethylene were prepared by impregnation of β-Ga2O3 with a palladium nitrate solution with following drying and reduction in a hydrogen flow at 200°C. A part of the samples was then calcined in an argon flow at 200–500°C. The as-prepared samples were tested in the reaction of selective liquid-phase hydrogenation of acetylene. EXAFS was used to study structure of the catalyst components. Based on the EXAFS data it was found that Pd–Ga alloys present in the subsurface region of Pd particles. The presence of these alloys increases activity and selectivity of catalysts. The alloys are decomposed by calcination in inert atmosphere following decrease in catalytic activity.

Characterization of the interface of two dental palladium alloys cast on a prefabricated implant gold cylinder

The interface between two dental alloys (Pd–Cu–Ga, Pd–Ga) cast-to a prefabricated gold cylinder in two thicknesses (1, 2 mm) was investigated. Specimens were observed in optical and scanning electron microscopes. Line scan microanalysis by EDS was performed and polarization curves were taken. Gold cylinders shape was preserved. Characteristic elongated grains were detected at the gold cylinder alloy. The boundaries between the cylinder and the cast-to alloys were distinct. The 2 mm thick Pd–Ga alloy cast to the gold cylinder revealed high porosity at the interface, while the rest of the subgroups showed no or negligible porosity. Line scan analysis revealed the gradual diffusion of the main elements of each alloy in the structure of the gold cylinder and vice-versa in a 3–5 μm zone. Corrosion behaviour was estimated by cyclic polarization tests in 1 M lactic acid. The polarization curves showed negative hysteresis. In the reverse anodic scan the current density was less than that for the forward scan. This fact confirms that all the tested materials are not susceptible to corrosion in 1 M lactic acid.

Effect of different high-palladium metal-ceramic alloys on the color of opaque and dentin porcelain

Statement of problem The color of dental porcelain depends on the type of metal substrate. Little research has been done to document the effects of different types of high-palladium alloys on the color of dental porcelain. Purpose The purpose of this in vitro study was to evaluate the effects of different high-palladium alloys on the resulting color of dentin porcelain, as well as on that of opaque porcelain after simulated dentin and glazing firing cycles. Material and methods Three Pd-Cu-Ga alloys, Spartan Plus (S), Liberty (B), and Freedom Plus (F), and 5 Pd-Ga alloys, Legacy (L), IS 85 (I), Protocol (P), Legacy XT (X), and Jelenko No.1 (N), were examined. A Pd-Ag alloy, Super Star (T), was included for comparison to the high-palladium alloys, and the Au-Pd alloy, Olympia (O), served as the control. Six cast discs (16 × 1 mm) were prepared from each of the alloys. Shade B1 opaque porcelain (Vita-Omega) was applied at a final thickness of 0.1 mm. After 2 opaque porcelain firing cycles, the surfaces were airborne-particle abraded, and the specimens were divided into 2 groups. In the first group, 0.9 mm of B1 dentin porcelain was applied. The other group of specimens with only opaque porcelain underwent the same dentin porcelain and glazing firing cycles. Color differences (ΔE) were determined with a colorimeter between the control and each experimental group, after the second opaque porcelain, second dentin porcelain, and glazing firing cycles. One-way analysis of variance and Dunnett's multiple range test were performed on the ΔE data (α=.05). Results After the application of dentin porcelain, the 3 Pd-Cu-Ga alloys showed significantly different ( P<.05) ΔE values (S = 2.3 ± 0.5, B = 1.4 ± 0.3, and F = 1.3 ± 0.7) than the control group. After the glazing cycle of this group, the 3 Pd-Cu-Ga alloys and the Pd-Ag alloy exhibited significantly different ( P<.05) ΔE values (S = 2.8 ± 0.8, B = 2.2 ± 0.3, F = 1.9 ± 1.0, and T = 1.4 ± 0.5) than the control group. After the simulated dentin porcelain firing cycles, the specimens with only opaque porcelain exhibited significantly different ( P<.05) ΔE values (S = 5.2 ± 1.4, B = 5.4 ± 0.6, and F = 3.9 ± 0.2) than the control group. The color difference between the 3 Pd-Cu-Ga alloys with only opaque porcelain and the control group increased more after the simulated glazing cycle (S = 6.6 ± 1.5, B = 6.3 ± 0.5, and F = 4.6 ± 0.1). The observed color differences between the Pd-Ga alloys and the control group were not statistically significant at any point. Conclusions The Pd-Cu-Ga alloys with only opaque porcelain, after the simulated dentin porcelain and glazing firing cycles, exhibited clinically unacceptable color differences. The application of dentin porcelain to the Pd-Cu-Ga alloys resulted in clinically acceptable color differences. The application of dentin porcelain to the Pd-Ag alloy, after the glazing firing cycle, resulted in clinically acceptable color differences (approximately 2.8 to 3.7 ΔE CIELAB units). The Pd-Ag alloy specimens with only opaque porcelain did not exhibit significant color differences from the control group, whereas significant color differences from the control group after the dentin porcelain and glazing firing cycles were still clinically acceptable.

A comparison of the porcelain fracture resistance of screw-retained and cement-retained implant-supported metal-ceramic crowns

Statement of problem The presence of a screw opening on the occlusal surface of implant-supported metal-ceramic crowns may decrease the porcelain fracture resistance and shorten the longevity of the crown. Purpose The purpose of this study was to compare the porcelain fracture resistance between screw-retained and cement-retained implant-supported metal-ceramic crowns and to assess whether narrowing the occlusal table or offsetting the screw-access opening affects fracture resistance. Material and methods Forty standardized maxillary premolar metal copings were fabricated with a Pd-Ga alloy (Protocol) on an implant abutment. Copings were divided into 4 groups (n=10): Group 1 (Screw-retained; occlusal surface buccolingual width=5 mm), screw access opening placed in the center of the occlusal surface; Group 2 (Screw-retained; occlusal surface buccolingual width = 5 mm), screw access opening positioned 1 mm offset from the center of the occlusal surface toward the buccal cusp; Group 3 (Cement-retained; occlusal surface buccolingual width = 5 mm), copings were not altered; and Group 4 (Cement-retained; occlusal surface buccolingual width = 4 mm), copings designed to have a reduced occlusal surface width. All castings were finished with aluminum oxide stones and airborne-particle abraded. Two layers of opaque and dentin porcelain were applied, respectively, on all specimens, which were then glazed. The crown specimens were positioned in a custom testing apparatus and vertically loaded on the middle of the occlusal surface with a universal testing machine at a crosshead speed of 0.5 mm/min until fracture. Mean values of load at fracture (Kgf) were calculated in each group and compared with a 1-way analysis of variance and Tukey's Studentized test (α=.05). Results Mean values of loads required to fracture the crowns were as follow: Group 1: 95.01±46.6 Kgf; Group 2: 108.61±57.9 Kgf; Group 3: 390.94±151.3 Kgf; Group 4: 380.04±211.8 Kgf. Groups 1 and 2 required a significantly lower force to fracture the crowns compared with Groups 3 and 4 ( P=.0001). Comparing Group 1 with 2 ( P=.9) and Groups 3 with 4 ( P=.6), no significant differences were noted. Conclusions Screw-retained implant-supported metal-ceramic crowns demonstrated a significantly lower porcelain fracture resistance than cement-retained crowns. Placing the screw access opening 1 mm offset from the center of the occlusal surface did not result in lower fracture resistance. Cement-retained crowns with 4- or 5-mm buccolingual width of the occlusal surface showed similar porcelain fracture resistance.

Transmission electron microscopic studies of deformed high-palladium dental alloys

Objective. The purpose of this study was to employ transmission electron microscopy (TEM) to investigate the microstructures of Pd–Cu–Ga and Pd–Ga dental alloys that had been permanently deformed, in order to obtain information about the deformation behavior of individual phases and changes in microstructure brought about by that deformation. Methods. Heavily deformed regions taken from fractured tensile test bars of the two alloys in the as-cast condition were prepared for TEM analysis, using mechanical grinding and polishing, ion milling, and plasma cleaning. The specimens were examined in the TEM using bright-field and dark-field diffraction contrast imaging. Selected-area and convergent-beam electron diffraction patterns were employed to analyze the structures of the phases, and standardless energy-dispersive X-ray spectrometry was used to determine their mean compositions. Results. For both alloys, tweed structures underwent permanent deformation by twinning, whereas dislocation movement occurred in the face-centered cubic (fcc) palladium solid solution matrix. A body-centered cubic (bcc) phase, previously unreported in our TEM studies and containing a high density of dislocations, was identified in the Pd–Cu–Ga alloy, while fine-scale, stress-induced precipitates were found in some regions of the fcc matrix in the Pd–Ga alloy. Significance. The present results have provided novel information about the mechanical deformation behavior of high-palladium alloys. The stress-induced precipitation in the Pd–Ga dental alloy studied may be a critical component of strengthening mechanisms.

Fatigue studies of high-palladium dental casting alloys: Part II. Transmission electron microscopic observations.

The microstructures of two representative high-palladium dental alloys, a Pd-Cu-Ga alloy and a Pd-Ga alloy, which had been subjected to cyclic fatigue in uniaxial tension were investigated by transmission electron microscopy (TEM). Two different mechanisms were found to dominate microplastic deformation during fatigue: twinning in the Pd-Cu-Ga alloy, and planar slip of dislocations in the Pd-Ga alloy. In addition, stress-induced precipitation occurred in the Pd-Ga alloy during cyclic loading. Heat treatment simulating the firing cycles for dental porcelain resulted in the formation of a previously unreported bcc phase in the Pd-Cu-Ga alloy, and in the elimination of the characteristic tweed structure found in the Pd-Ga alloy for the as-cast condition.

Fatigue studies of high-palladium dental casting alloys: Part I. Fatigue limits and fracture characteristics.

The fatigue limits and fracture characteristics for a Pd-Cu-Ga alloy and a Pd-Ga alloy were studied. The alloys were cast into tensile test bars with gauge diameter of 3 mm and gauge length of 15 mm, and the surfaces of the castings were neither air-abraded nor polished after removal from the investment. Specimens were prepared from all-new metal (not previously melted), a combination of 50% new metal and 50% old metal (previously melted one time) and 100% old metal. The cast bars were subjected to heat treatment simulating the complete firing cycles for dental porcelain, and fatigued in air at room temperature under uniaxial tension-compression stress at 10 Hz and a ratio of tensile stress amplitude to compressive stress amplitude (R-ratio) of -1. The alloy microstructures and fracture surfaces were examined with a scanning electron microscope (SEM). Results showed that the fatigue limits at 2 x 10(6)cycles of the Pd-Cu-Ga and Pd-Ga alloys were approximately 0.20 and 0.15 of their 0.1% yield strength (YS) in tension, respectively. The fatigue resistance for specimens from both alloys containing 50% old metal and 50% new metal was comparable to that of specimens containing all-new metal, although this decreased dramatically for Pd-Cu-Ga alloy specimens containing all-old metal. The fatigue resistance of the Pd-Cu-Ga alloy subjected to heat treatment simulating the porcelain firing cycles was not adversely affected by remnants of the original as-cast dendritic microstructure that remained in the relatively large test specimens. A longer heat treatment than recommended by the manufacturer for the porcelain firing cycles is needed to completely eliminate the as-cast dendritic structure in these specimens. The Pd-Cu-Ga alloy exhibited superior fatigue resistance to the Pd-Ga alloy, which has an equiaxed-grain microstructure and lower yield strength.

Inductively coupled plasma-mass spectroscopy measurements of elemental release from 2 high-palladium dental casting alloys into a corrosion testing medium

Statement of Problem. The biocompatibility of high-palladium alloy restorations has been of some concern due to the release of palladium into the oral environment and sensitivity reactions in patients. Purpose. This study measured the in vitro elemental release from a Pd-Cu-Ga alloy and a Pd-Ga alloy into a corrosion testing medium. Material and Methods. Both alloys were cast into 12-mm-diameter × 1-mm-thick disks, subjected to heat treatment that simulated porcelain firing cycles, polished to a 0.05-mm surface finish, and ultrasonically cleaned in ethanol. Two specimens of each alloy were immersed 3 times (at 7, 70, and 700 hours) in an aqueous lactic acid/NaCl solution used for in vitro corrosion testing and maintained at 37°C. The specimens were removed after each immersion time, and the elemental compositions of the solutions were analyzed with inductively coupled plasma-mass spectroscopy (ICP-MS). Elemental concentrations for the 2 alloys at each immersion time were compared with Student t test (α=.05). Results. No significant differences in palladium release were found for the 7- and 70-hour solutions, but significant differences were found for the 700-hour solutions. Mean concentrations of palladium and gallium in the 700-hour solutions, expressed as mass per unit area of alloy surface, were 97 (Pd) and 46 (Ga) μg/cm2 for the Pd-Cu-Ga alloy and 5 (Pd) and 18 (Ga) μg/cm2 for the Pd-Ga alloy. Conclusion. Relative proportions of the elements in the solutions were consistent with the release of palladium and breakdown of microstructural phases found in the alloys. The results suggest that there may be a lower risk of adverse biological reactions with the Pd-Ga alloy than with the Pd-Cu-Ga alloy tested. (J Prosthet Dent 2002;87:80-5.)

Potentiodynamic polarization study of the in vitro corrosion behavior of 3 high-palladium alloys and a gold-palladium alloy in 5 media

Statement of Problem. Corrosion of cast alloy restorations may lead to their failure or adversely affect their biocompatibility. Although some documentation of the corrosion behavior of the high-palladium dental alloys exists, questions remain about their corrosion resistance and mechanisms. Purpose. This study compared the in vitro corrosion characteristics of 3 high-palladium alloys and 1 gold-palladium alloy in simulated body fluid and oral environments. Material and Methods. Two Pd-Cu-Ga alloys and 1 Pd-Ga alloy were selected; an Au-Pd alloy served as the control. The corrosion behavior for the as-cast and simulated porcelain-firing (heat-treated) conditions of each alloy (N = 5) was evaluated in 0.9% NaCl, 0.09% NaCl, and Fusayama solutions. Heat-treated specimens of each alloy (N = 5) were also tested in N2-deaerated 0.09% NaCl and Fusayama solutions (pH 4). After immersion in the electrolyte for 24 hours, the open-circuit potential (OCP) was measured, and linear polarization was performed from −20 mV to +20 mV (vs. OCP) at a scanning rate of 0.125 mV/s. Cyclic polarization was performed from −300 mV to +1000 mV and back to −300 mV (vs. OCP) at a scanning rate of 1 mV/s. Data were evaluated with analysis of variance and the Ryan-Einot-Gabriel-Welsch multiple-range test (α=.05). Results. The OCP of each alloy varied with the condition (as-cast or heat-treated) and electrolyte used. Corrosion resistance was similar for the 4 alloys tested. For cyclic polarization, all alloys showed active-passive or spontaneous passive behavior in nearly all electrolytes. During some reverse scans, the 3 high-palladium alloys displayed 3 or 5 anodic peaks. No positive hysteresis was observed for any of the alloy/electrolyte combinations evaluated. Conclusion. The corrosion resistances of the 3 high-palladium alloys in simulated body fluid and oral environments were comparable to that of the gold-palladium alloy. The similar corrosion resistance for the 3 high-palladium alloys was attributed to their high noble metal content and theorized stable structure at the submicron level. Selective corrosion of different phases and elements, surface enrichment of palladium, and adsorption of species are possible corrosion mechanisms. The cyclic polarization results suggest that none of the 4 alloys would be prone to pitting or crevice corrosion under in vivo conditions, but crevice conditions should nonetheless be avoided for these alloys in the oral environment. (J Prosthet Dent 2002;87:86-93.)

Effect of different high-palladium metal-ceramic alloys on the color of opaque porcelain.

The purpose of this study was to assess the effect of different high-palladium alloys on the resulting color of opaque porcelain. Three Pd-Cu-Ga alloys, Spartan Plus (S; Williams Dental Co/Division of Ivoclar North America, Amhest, NY), Liberty (B; J.F. Jelenko & Co, Armonk, NY), and Freedom Plus (F; J.F. Jelenko & Co); 4 Pd-Ga alloys, Legacy (L; J.F. Jelenko & Co), IS 85 (I; Williams Dental Co), Protocol (P; Williams Dental Co), and Legacy XT (X; J.F. Jelenko & Co); and a Pd-Ag alloy, Super Star (T; J.F. Jelenko & Co), were examined. The Au-Pd alloy Olympia (O; J.F. Jelenko & Co) served as the control. Three cast 16-mm discs, 1-mm thick, were prepared from each of the alloys. After metallurgically polishing and air-abrading, the specimens were oxidized following the manufacturer's recommendations. Shade B1 opaque porcelain (Vita-Omega; Vident, Baldwin Park, CA) was applied at a final thickness of 0.1 mm using a mold. After 2 opaque porcelain firing cycles, the surfaces were air-abraded. The colors of the specimens were measured using a colorimeter and expressed in Commission International de l'Eclairage (CIE) L*a*b* coordinates. Color differences (delta E) were determined between the control and each experimental group. Analysis of Variance and Tukey-Kramer tests were performed on the delta E data. The 3 Pd-Cu-Ga alloys showed significantly greater (p < .01) delta E values (S = 2.8 +/- 1.1, B = 3.0 +/- 0.6, and F = 2.1 +/- 0.2) than the remaining 5 experimental groups (L = 0.7 +/- 0.5, I = 0.7 +/- 0.4, P = 0.7 +/- 0.2, X = 0.7 +/- 0.4, and T = 0.7 +/- 0.5). The directions of the significant color changes were relatively equally distributed along the L*, a*, and b* axes, and all delta L*, delta a*, and delta b* values were negative (lower value, more green and blue relative to control O). This work suggests that a 0.1-mm-thick layer of opaque porcelain in the Pd-Cu-Ga alloys studied, did not reliably reproduce the color of porcelain.

Electrochemical characteristics of high-Pd alloys in relation to Pd-allergy

Objective: The aim of this study was to determine whether the Pd–Cu-based dental ceramic alloys possess any electrochemical characteristics distinguishable from that of other Pd-containing alloys. Of all Pd-containing alloys, this particular alloy group has been linked to frequent incidence of allergy and hypersensitivity reactions. Electrochemical corrosion may instigate these reactions. Methods: Four groups of alloys, Pd–Cu, Pd–Ga-(with and without Ag), Pd–Ag, and Au–Pd, were evaluated by traditional corrosion measurement techniques in a phosphated buffer saline solution at 20°C. The electrochemical characteristics measured were: (1) 20 h open circuit potential (OCP); (2) 20 h corrosion rate ( I corr); and (3) anodic polarization ( E– i) curves. Results: The OCP values (232±25 mV) of the Ag-free Pd–Ga and Pd–Cu-based alloys were higher than and distinctly different from that (144±52 mV) of the Ag-containing alloys. The I corr values of different alloys, despite varied compositions, were indistinguishable from one another. The E– i curves of all alloys were essentially similar, with the Ag-containing (>5 wt%) alloys showing a subtle difference in their anodic slope within 100 mV above their corrosion potentials. Significance: The OCP values of Pd–Cu alloys and the Ag-free Pd–Ga alloy are comparable to that reported for pure Pd (239±21 mV), which indicates that during corrosion these alloys undergo dealloying and consequent Pd-enrichment on their surface. Such a condition is conducive to the release of allergenic Pd ++ ions and offers a plausible explanation for the frequent incidence of hypersensitivity reactions associated with the Pd–Cu alloys. The OCP values in other alloys are attributed to dealloying followed by surface enrichment with Ag and/or Au and the possible formation of an insoluble AgCl surface film on the respective alloy surfaces. These events have the potential to suppress or prevent Pd ++ ion release. Alloys showing these characteristics have seldom been linked to allergic reactions.